Climate warming and tree carbon use efficiency in a whole‐tree ¹³CO₂ tracer study

Abstract

Summary Autotrophic respiration is a major driver of the global C cycle and may contribute a positive climate warming feedback through increased atmospheric concentrations of CO2. The extent of this feedback depends on plants' ability to acclimate respiration to maintain a constant carbon use efficiency (CUE). We quantified respiratory partitioning of gross primary production (GPP) and CUE of field‐grown trees in a long‐term warming experiment (+3°C). We delivered a 13C–CO2 pulse to whole tree crowns and chased that pulse in the respiration of leaves, whole crowns, roots, and soil. We also measured the isotopic composition of soil microbial biomass and the respiration rates of leaves and whole crowns. We documented homeostatic respiratory acclimation of foliar and whole‐crown respiration rates; the trees adjusted to experimental warming such that leaf‐level respiration rates were not increased. Experimental warming had no detectable impact on respiratory partitioning or mean residence times. Of the 13C label acquired by the trees, aboveground respiration consumed 10%, belowground respiration consumed 40%, and the remaining 50% was retained. Experimental warming of +3°C did not alter respiratory partitioning at the scale of entire trees, suggesting that complete acclimation of respiration to warming is likely to dampen a positive climate warming feedback.

Clues for our missing respiration model

“…The results from the Drake et al . () study show no difference in CUE in response to higher temperature at the whole tree level. CUE did not vary with site mean annual temperature for sites that compared CUE across sites (Fig.…”

“…Warming did not affect the maintenance respiration rate or the relationship between growth respiration and biomass growth. The second study found that +3°C warming did not alter the fraction of canopy photosynthesis used for respiration and growth, or the residence time of C in various tree components (Drake et al ., ). Thus, warmer chambers grew larger trees that captured more C and grew more, with no change in carbon use efficiency (CUE, 1 – respiration/photosynthesis, or the ratio of growth to photosynthesis).…”

“…Drake et al . () produced strong evidence that respiration indeed acclimates at the whole‐tree level in response to warming. This result emphasizes the need for advances in models of respiration, with realistic acclimation functions, to predict the response of respiration to environmental change.…”

“…Also in this issue of New Phytologist , Drake et al . (, pp. 1313–1324) expand on the first study by using carbon‐13 ( 13 C) labelling to determine if the fraction of photosynthesis used for respiration changes in response to the c .…”

“…(b) Chambers used in the Drake et al . (,b in this issue of New Phytologist , pp. 1299–1313 and 1313–1324) experiments in the context of the surrounding plantation.…”